The present invention relates to an improved carburetor, and, more particularly, to an improved air valve carburetor in which the air valve is a circular valve pivoted around one of its diameters.
Variable air valve type carburetors are known for providing fuel-air mixture for internal combustion engines. Their construction is complicated, but they possess good metering, particulation, and atomization characteristics, over a wide range of air flow amounts.
FIGS. 1, 2, and 3 show various prior art air valve carburetors. In these carburetors, an air valve 3 is provided upstream of a throttle valve 1, and the air valve 3 is controlled by a diaphragm device 2 according to the vacuum between the air valve 3 and the throttle valve 1, in a feedback manner, so as to maintain this vacuum level always substantially constant. Further, a jet needle 5 is inserted into a fuel nozzle 4, through which fuel is sucked by this vacuum Po between the air valve 3 and the throttle valve 4. The jet needle 5 is moved by the motion of the air valve 3, so that the effective cross-sectional area of the nozzle 4 is increased along with the opening of the air valve 3, so as to control the flow of fuel in direct proportion to the flow of intake air, thereby maintaining a constant air/fuel ratio.
In the carburetors shown in FIGS. 1 and 2, the air valves 3 have rectangular vanes 3a and 3b. In FIG. 1 the base of the vane 3a is pivoted to the side of the air passage 6; and in FIG. 2 the arm portion of the vane 3b is pivoted to the wall of the carburetor body 7. In both of these carburetors, it is difficult to control precisely the air/fuel ratio, because the aperture for the rotation of the vanes 3a and 3b cannot be precisely set, and the quality thereof is rather unstable.
In the carburetor of FIG. 3, the air valve is a circular plate which is pivoted about one of its diameters. Thus the abovementioned problem is overcome. However, the complicated link mechanism 8 for linking the jet needle 5 and the air valve 3 means that changes of the mechanism over time, such as caused by wear, affect badly the control of the air/fuel ratio, resulting in problems reating to durability of the carburetor, and the like.
Because of the fact that the momentum force about the supporting axis of vanes of FIGS. 1 and 2 caused by the air stream are not balanced, there is a risk that these vanes may be disturbed, bent, or broken, due to the large momentum force which occurs during accelation or backfiring of the engine.